One type of acoustic device uses a bone conduction technique that causes a user to hear sound by contacting a vibrating body to the user's auricle, such as the tragus or the like of the ear (for example, see JP 2005-348193 A (PTL 1)). An acoustic device using a bone conduction technique transmits vibration directly to the auditory nerve and thus places little strain on the eardrum. Such an acoustic device is therefore better than an earphone, headphone, or other acoustic device that does not use a bone conduction technique.